A tractor operated 12 \(\times\) 60 cm boom sprayer had an overlap of 30 cm between the successive passes during field operation at an average speed of 4.2 km h\(^{-1}\). A total time loss of 7.5 min ha\(^{-1}\) was observed during turnings. Assuming no overlap of spray material between adjacent nozzles, the field efficiency of the sprayer in per cent is _____.
\textit{[Round off to two decimal places.]}